Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface showing our new design.

The broken lines in the FIGURE show portions of the display screen or portion thereof with a graphical user interface which form no part of the claimed design.

The dot-dash lines in the FIGURE represent a display screen and boundary line, and form no part of the claimed design. 

CLAIM We claim the ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 